Exposure method

ABSTRACT

An exposure method wherein a mask on which a pattern is formed is illuminated with a slit-like illumination light beam, and the mask and a substrate are caused to scan the slit-like illumination light beam in a scanning direction in order to form an image of the pattern on the substrate, and wherein photo-electric signals obtained by a sensor which moves in the scanning direction, relative to the slit-like illumination light beam, and photo-electric signals obtained from the sensor which moves in a direction orthogonal to the scanning direction are integrated so as to obtain integrated values thereof, and an unevenness among the integrated values relating to a direction orthogonal to the scanning direction is calculated

This is a continuation of application Ser. No. 08/354,716 filed Dec. 6,1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of measuring an unevenness inexposure, and also to an exposure method using this measuring method,which can be suitably applied for an exposure process with the use of,for example, the so-called step-and-scan type exposure apparatus or theso-called slit-scan exposure type exposure apparatus wherein a reticleand a wafer scan a slit-like illumination area in synchronization witheach other so as to sequentially expose a pattern on the reticle ontoshot areas on the wafer

2. Related Background Art

Heretofore, there has been used a projection exposure apparatus for amanufacture of a semiconductor element, a liquid crystal displayelement, a thin film magnetic head or the like with the use of aphotolithographic process, in which a photomask or a reticle (which willbe hereinbelow representatively denoted as "reticle") is illuminated byan illumination optical system so as to project and expose a pattern onthe reticle onto a wafer (or a glass plate or the like) coated thereoverwith a photoresist through a projection optical system As one ofcharacteristics for evaluating such a projection exposure apparatus, theso-called image plane unevenness in exposure caused by unevenness intransmissivity of the illumination optical system or the projectionoptical system has been raised. Due to this unevenness in exposure, thewidth of lines of a pattern exposed onto the wafer have differed from adesired value, and accordingly, it has been required to confine thisunevenness in exposure within a tolerable range during the exposure.

Accordingly, it has been required to precisely measure an unevenness inexposure For example, in a conventional batch exposure type projectionexposure apparatus (such as a stepper), an evenness in exposure has beenmeasured as follows: a photo-electric conversion element (which will behereinbelow denoted as "illumination sensor") such as a photomultiplieror a photodiode having a pin-hole like light receiving part, is set on awafer stage on which a wafer is mounted. A photo-electric conversionelement (which will be hereinbelow denoted as "integrator sensor") suchas a photomultiplier or a photodiode for receiving a slight volume oflight taken out from illumination light in an illumination opticalsystem is provided in the illumination optical system The reason why thelater-mentioned photo-electric conversion element is called anintegrator sensor, is that the integrated exposure value over a wholeexposure field on the wafer can be known from an integrated value of anoutput signal from the photo-electric conversion element.

Further, conventionally, the illumination sensor has been moved toseveral points to be measured in the exposure field defined by theprojection optical system, and accordingly, output signals from theillumination sensor have been integrated over the respective actualexposure time lengths. In this case, in order to eliminate affection bya variation in light emitting energy from a light source between pointsto be measured, the integrated value of the output signals from theintegrator sensor has been also measured, and the integrated value ofthe output signals from the illumination sensor 18 has been divided bythe integrated value of output signals from the integrator sensor fornormalization An unevenness in exposure within the exposure field hasbeen measured from the thus obtained uneven integrated values of theoutput signals which have been normalized, for each of the measuringpoints. Further, these measuring points have been distributed in adesired area within the exposure field in order to measure an unevennessin an arbitrary area.

Recently, there has been a tendency to increase the chip size of asemiconductor element, and accordingly, large area exposure has beenrequired for an exposure apparatus in order to expose a pattern having alarger area onto a wafer from a reticle. Further, there is a limitationon design and manufacture in order to increase the size of an exposurefield defined by a projection optical system In order to increase thearea of a pattern to be exposed and in order to cope with the limitationto the size of the exposure field defined by the projection opticalsystem, the so-called step-and-scan type and slit-scan exposure typeprojection exposure apparatuses (which will be hereinbelowrepresentatively denoted as "scan exposure system") in which a reticleor a wafer scans an illumination area (which will be hereinbelow denotedas "slit-like illumination area") whose shape is rectangular, arcuate,hexagonal or the like so as to sequentially expose a pattern on thereticle onto shot areas on the wafer, have been developed.

Even in such a scan-exposure type projection exposure apparatus, it isrequired to confine unevenness in exposure on a wafer within anallowable range after exposure by the scan exposure system, theunevenness in exposure is one of important evaluation characteristics Inthis regard, the scan exposure system also offers such a disadvantage inthat an actual unevenness can not be measured after scan exposure onlyby measuring a static unevenness in exposure within an exposure fielddefined by a projection exposure system, as is in the case of a batchexposure system.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above-mentionedmatters, and accordingly, one object of the present invention is tomeasure an illumination distribution of light while a sensor is moved.

Another object of the present invention is to provide a method ofmeasuring an evenness in exposure, which can precisely measure anevenness in exposure on a wafer even after exposure by a scan exposuresystem with the use of a scan exposure type exposure apparatus. Further,another object of the present invention is to provide a scan exposuretype exposure method using the above-mentioned measuring method.

According to the present invention, photoelectric signals are obtainedfrom a sensor which is moved in a predetermined scanning direction, andthen an unevenness among photo-electric signals (integrated values ofphoto-electric signals) substantially orthogonal to the scanningdirection is obtained in accordance with the thus-obtainedphoto-electric signals.

According to one aspect of the present invention, there is provided amethod comprising the steps of: obtaining photo-electric signals from asensor while moving the latter in a predetermined scanning direction;repeating the scanning of the sensor after moving the sensor in adirection substantially orthogonal to the scanning direction, andintegrating photo-electric signals obtained during each scanning; andcalculating an unevenness among the thus integrated values of thephoto-electric signals relating to a direction orthogonal to thescanning direction

Further, according to another aspect of the present invention, there isprovided an exposure apparatus comprising: an illumination opticalsystem for illuminating a mask on which a pattern is formed, with aslit-like illumination light beam; a mask stage for moving the mask; asubstrate stage for moving a substrate on which an image of the patternis formed; a drive device for scanning the mask and the substraterelative to the slit-like illuminating light beam; a sensor provided onthe substrate stage; a controller for controlling the drive device so asto move the substrate stage in a scanning direction and a directionorthogonal to the scanning direction; and a calculating device forcalculating an integrated value of outputs from the sensor for eachscan, and calculating an evenness among the integrated values relatingthe direction orthogonal to the scanning direction

Further, according to another aspect of the present invention, there isprovided a method of measuring an intensity of illumination, used in amanufacture of a semiconductor device, comprising the steps of:

illuminating a substrate from which the semiconductor device is formed,with a slit-like illumination light beam;

delivering a photo-electric signal from a sensor while moving the latterin the direction of the scanning, relative to the slit-like illuminationlight beam;

repeating the scanning of the sensor after moving the sensor in adirection orthogonal to the scanning direction;

integrating the photo-electric signals obtained during each scanningcycle; and

calculating an unevenness among integrated values of the photo-electricsignals relating to the direction orthogonal to the scanning direction

Further, according to another aspect of the present invention, there isprovided an exposure method comprising the steps of: illuminating a maskon which a pattern is formed, with a slit-like illumination light beam;

scanning said mask and a substrate so as to form an image of a patternon the substrate;

delivering an output signal from a sensor while moving the latter in ascanning direction with respect to the slit-like illumination lightbeam;

using an array sensor in which a plurality of photo-electric conversionelements are arrayed in a direction orthogonal to the scanningdirection, as the sensor, and integrating photo-electric signals whichare obtained from the respective photo-electric elements; and

calculating an unevenness among integrated values of the photo-electricsignals relating to a direction orthogonal to the scanning direction

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view including a perspective view in part, andillustrating a step-and-scan type projection exposure apparatus in oneembodiment of the present invention;

FIG. 2A is a view showing an evenness in illumination intensity in aslit-like exposure area 16 in a static condition;

FIG. 2B is a view showing a distribution of integrated exposure valuesin a nonscanning direction after scanning exposure;

FIG. 3 is an explanatory view in the case of repetitions of scanning ofan illumination sensor 18 with respect to the slit-like exposure area16;

FIG. 4 is a view showing integrated output signals from the illuminationsensor 18, which are obtained during measuring shown in FIG. 3, andwhich are lined up in a nonscanning direction;

FIG. 5 is a view showing signals which are normalized by dividing theintegrated output signals from the illumination sensor 18 withintegrated output signals from an integrator sensor 7, and which arelined up in a nonscanning direction; and

FIG. 6 is an explanatory view in the case of causing a line-sensor typeillumination sensor 21 to scan once the slit-like exposure area 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Explanation will be hereinbelow made of an embodiment of the presentinvention with reference to FIGS. 1 to 5. In this embodiment, thepresent invention is applied to an exposure process using astep-and-scan type projection exposure apparatus in which a pulsed laseris used as a light source for illumination light. It is noted that sincethis embodiment uses a pulsed light source, the exposure energy per eachpulse which is irradiated onto a wafer will be denoted simply as"exposure dose", and the accumulated value of exposures irradiated ontoa point on the wafer by plural cycles of pulsed exposure per scanningcycle will be denoted as "integrated exposure value". This integratedexposure value is the same as an exposure value obtained by using acontinuously emitting light source (such as continuous wave laser or amercury lamp) as an exposure light source.

Referring to FIG. 1 which is a schematic view illustrating a projectionexposure apparatus in this embodiment, a deep UV laser beam LB₀ (havinga wavelength of, for example, 248 nm) emitted from an excimer lasersource 1 is incident upon a beam shaping optical system 3 by way of amirror 2 so as to be shaped into a laser beam LB₁ having across-sectional shape corresponding to the shape of a fly-eye lens 4 asan optical integrator Several light source images are formed on theemission side focal plane of the fly-eye lens 4, and an aperture stop(which will be hereinbelow denoted as "σ-stop") 5 is located in theemission side focal plane

Illumination light emitted from the several light source images in theaperture area of the σ-stop 5 is incident upon a beam splitter 6 forlight-branching. A part of the illumination light is reflected by thebeam splitter 6, and is then incident upon the light receiving surfaceof an integrator sensor 7 which delivers an output signal S to acalculating device 8. A proportional coefficient between the outputsignal from the integrator sensor 7 and an exposure energy on a wafer Whas been beforehand stored in memory in the calculating device 8.Accordingly, the calculating device 8 integrates output signals S fromthe integrator sensor 7 in order to monitor an integrated exposure valueon a wafer W. A PIN type photo diode, a photomultiplier or the likewhich is highly sensitive to deep-ultraviolet radiation can be used asthe integrator sensor 7.

Illumination light transmitted through the beam splitter 6 illuminates arectangular illumination area 14 on a reticle R by way of a first relaylens 9, a reticle blind 10 as a field stop, a second relay lens 11, amirror 12 for deflecting a light path, and a main condenser lens 13.Accordingly, an image of a pattern in the illumination area 14 isprojected and focused onto a rectangular exposure area 16 on the wafer Wthrough a projection optical system PL. As shown in FIG. 1, the Z-axisis taken in parallel with the optical axis of the projection opticalsystem, and the X-axis in the XY plane orthogonal to the optical axis istaken in the direction of the short-side of the rectangular illuminationarea 14.

In this case, the reticle R is held on a reticle stage 15 which causesthe reticle R to scan in the X or -X direction at a predetermined speedby a motor (a step motor, a linear motor or the like) 30. Meanwhile, thewafer W is held on a wafer stage 17 which positions the wafer W in theXY plane by a motor (a step motor, a linear motor or the like) 31 andwhich is composed of an XY stage scanning in the X or -X direction at apredetermined speed, a Z-stage for positioning the wafer W in the Zdirection, and the like. A controller 100 controls the degrees ofrotation of the motors 30, 31 so as to control the relative movementbetween the reticle R and the wafer W.

Further, estimating that the projection magnification of the projectionoptical system PL is β (for example 1/4), the wafer stage 17 is at firstsubjected to stepping drive so as to set a next shot area SA to beexposed on the wafer W at an exposure initiating position in order tocarry out exposure in a scan exposure system, and thereafter, the waferstage 17 causes the shot area SA on the wafer W to scan the exposurearea 16 in the -X direction (or X direction) at a speed V_(W) (V_(W)=β·V_(R)) in synchronization with the scanning of the reticle R in theX-direction (or -X direction) with respect to the illumination area 14by means of the reticle stage 15. Accordingly, an image of a circuitpattern on the reticle R is projected and exposed sequentially onto shotareas SA on the wafer W.

Further, an exposure unevenness sensor (which will be denoted as"illumination sensor") 18 composed of photo-electric conversion elementseach having a pin-hole like light receiving part is located in thevicinity of the wafer W on the wafer stage 17. A PIN type photodiode, aphotomultiplier or the like which is highly sensitive todeep-ultraviolet radiation, can be used as the illumination sensor 18,and an output from the illumination sensor 18 is delivered to thecalculating device 8 in the controller 100. The calculating device 8obtains a distribution of integrated exposure values and an evenness onthe wafer W after exposure by the scan exposure system as explainedbelow.

Accordingly, referring to FIGS. 2A and 2B, explanation will be made ofthe method, in this embodiment, of measuring an evenness amongintegrated exposure values, which possibly occurs in each shot-area onthe wafer, during exposure by the scan exposure system. When carryingout this measurement, the reticle R is removed from the reticle stage 15in FIG. 1. Alternatively, a plane glass pane having no pattern is set onthe reticle stage 15. In this embodiment, no measurement in which a testprint is used so as to handle a photoresist as a two-dimensional sensoris carried out. Should the test print be used so that an integratedexposure value on the wafer coated thereover with the photoresist andset on the wafer stage 17 is measured after scanning of the wafer W,with respect to the exposure area 16, only data containing an evennessin the coating of the photoresist, an evenness in sensitivity and thelike would be obtained, and accordingly, it is difficult to carry outprecise measurement.

In this embodiment, the illumination sensor 18 on the wafer stage 17shown in FIG. 1 scans the slit-like exposure area 16 so as to measure anintegrated exposure value in each shot area on the wafer W. Actually,when the exposure is made by the scan exposure system, a factor causingan evenness in the integrated exposure value which possibly occurs inthe entire surface of the shot area, differs from an evenness intransmissivity of an optical system in the case of a conventionalexposure type in which the measurement is made in a static condition.

Referring to FIG. 2A, which shows a curve 19 of illuminationdistribution in the slit-like illumination exposure area 16, the curve19 of illumination distribution exhibits a distribution e(X, Y) causedby an evenness in the transmissivity of the illumination optical systemand the projection optical system PL. The distribution e (X, Y) gives anintensity of illumination at a coordinate (X, Y) position. In the caseof a conventional exposure system, the distribution of exposure on thewafer W could be simply obtained only by measuring the distribution e(X,Y). However, in the case of the scan exposure system, the integratedexposure value E_(i) at a point Q in FIG. 2A, is obtained by integratingthe intensity of illumination over the exposure area 16 along a straightline 20 which passes through the point Q and which is in parallel withthe scanning direction (X direction).

That is, a value k·A_(i) where A_(i) is a cross-sectional area of thecurve 19 of illumination distribution in a plane through which thestraight line 20 passes, and k is a predetermined proportionalcoefficient, gives an integrated exposure value E_(i) at the point Q.FIG. 2B shows the result of the measurement of the integrated exposurevalue E_(i) in the Y direction (nonscanning direction). It is noted thatthe result of integrating the values on the curve 19 of illuminationdistribution at sampled points arranged along the straight line 20 isused, instead of the cross-sectional area A_(i) since the pulsedemission is used in this embodiment.

These sample points vary in dependence upon an unevenness in thescanning speed of the wafer stage 17, an evenness in the emission timingof the pulsed laser beam source or the like. Further, the relative valueof the curve 19 of illumination distribution shown in FIG. 2A, variesalso in dependence upon an evenness in emission energy at every pulsedillumination of the pulsed laser source. That is, the main factor of theunevenness in the integrated exposure value E at points on the wafer Wis an unevenness in the distribution of illumination in the slit-likeexposure area 16, and further, an unevenness in emission energy at evenpulsed emission of the pulse laser source, an error in the displacementof the wafer stage 17 during pulsed emission (an unevenness in speed), ajitter of the emission timing also possibly become factors of theunevenness in the integrated exposure value E in the scanning directionon the wafer W. Further, during the control of the exposure value, thescanning speed of the wafer stage 17 is determined with the use of thewidth (the so-called slit width) as one of terms, and accordingly, anerror in measuring the slit width also causes an unevenness in theintegrated exposure value in the scanning direction. In addition,factors caused steady-stately, or factors caused randomly (probabilisticfactors) are considered to be so.

There are various factors causing such an unevenness in the integratedexposure value in each shot area on the wafer W, and accordingly, it isdifficult to obtain an unevenness in the integrated exposure value forevery individual factor. In this embodiment, as shown in FIG. 1, thewafer stage 17 is driven so as to cause the illumination sensor 18 torepeatedly scan the slit-like exposure area 16 in the scanning direction(X direction) in order to measure an actual integrated exposure value.

It is noted that a minimum number N_(min) of exposure pulses to beirradiated onto each of points on the wafer W has been regulated inorder to give a predetermined reproducibility for the integratedexposure given to each of the points on the wafer W in such a case thata pulsed laser source having a predetermined unevenness in energy atevery pulsed emission, is generally used as the light source. Thisminimum number N_(min) of exposure pulses is determined in dependenceupon the degree of an unevenness in energy in each pulsed emission ofthe pulsed laser source. Further, when each of the points on the wafer Wis irradiated with the minimum number N_(min) of emission pulses, anunevenness in the integrated exposure values becomes largest.Accordingly, in order to carry out the measurement in such a conditionthat the evenness in the integrated exposure value becomes largest, themeasurement is carried out in such a condition that each of the pointson the wafer W is exposed by the minimum number N_(min) of exposurepulses, that is, the measurement is carried out by causing the waferstage 17 to scan at a maximum speed during the exposure (a maximum speedbe used to expose). As mentioned above, the function of the device isthus checked. Further, it goes without saying that by similarly carryingout a measurement at an arbitrarily set exposure speed (scanning speed),an unevenness (value) in exposure at the associated set exposure value(scanning speed) can be measured.

More specifically, since the illumination light is pulsed laser, theexposure value on the substrate W, is an energy obtained by integratingexposure energies each obtained at every pulsed emission within anexposure area corresponding to the illumination area 14. In general, anunevenness in emission energy at every pulsed emission is present at thepulsed light source. An averaged pulse exposure energy on the substrateW at every pulsed light is set to p, and a range of unevennesses in thepulse exposure energy of the pulsed light is set to δp.

Further, it is estimated that the parameter δp/p which gives anunevenness in the pulsed exposure energy is normally (randomly)distributed, if the number of light pulses irradiated onto each of thepoints on the substrate W is set to N, the component ΔE_(th) of anunevenness in the exposure, among theoretical unevennesses in theintegrated exposure value after completion of the exposure, is given by(δp/p)/N^(1/2). Accordingly, the worst value ΔE_(max) and thetheoretical unevenness ΔE_(th) has the following relationship Further,the value of ΔE_(th) is beforehand regulated in general in order toadvantageously cope with occurrence of an hindrance.

    ΔE.sub.max ≧(ΔE.sub.th.sup.2 +ΔE.sub.ot.sup.2).sup.1/2                           EX 1

where ΔE_(ot) is a component of an unevenness in exposure caused by scanexposure (including an unevenness in the intensity of illumination inthe scanning direction in a static condition, an emission jitter, anevenness in the speed of the stage, and the like)

In the above-mentioned expression, ΔE_(max) is known from themeasurement according to the present invention, and ΔE_(th)=(δp/p)/N^(1/2) can be obtained from, for example, an unevenness in theintegrated energy distribution (three times standard deviation) whichcan be obtained at relative scanning by branching and receiving thepulsed illumination light. It is noted that although the expression EX1is given the sum of squares, the more severe condition, that is,ΔE_(max) ≧(ΔE_(th) +ΔE_(ot)) can be used. With the use of the expressionEX1, the maximum value of ΔE_(ot) can be given as follows:

    ΔE.sub.ot =(ΔE.sub.max.sup.2 -ΔE.sub.th.sup.2).sup.1/2EX2

With the use of ΔE_(ot) in the expression EX2, if an allowable value(desired given value) of an unevenness in exposure in the case of theexposure by the scan exposure system at each of the points on thesubstrate W, is newly set to ΔE_(max) ', the following relationship canbe given:

    (δp/p)/N.sup.1/2 =ΔE.sub.th.sup.1/2 ≦(ΔE.sub.max '.sup.2 -ΔE.sub.ot.sup.2).sup.1/2                   EX 3

Accordingly, the minimum Number N_(min) of exposure pulses is a minimuminteger which can satisfy the following expression:

    N.sub.min =N≧(δp/p).sup.2 /(ΔE.sub.max '.sup.2 -ΔE.sub.ot.sup.2)                                   EX4

Referring to FIG. 3 which shows an scanning condition of theillumination sensor 18 in the case of the measurement of an unevennessin the integrated exposure value in this embodiment, the pin-hole-likelight receiving area 18a of the illumination sensor 18 sequentially scanthe slit-like exposure area 16 along a plurality of loci T1 to Tn (n isan integer more than 2) which are parallel with the scanning directionor the X direction. The loci T1 to Tn are arranged at substantiallyequal intervals in a nonscanning direction that is, a directionorthogonal to the exposure area, and accordingly the coordinate valueY_(i) in the Y-coordinate of each locus Ti (i=1 to n) has been measured.In this phase, the wafer stage 17 scans at the maximum speed during theexposure, and accordingly, pulsed light is irradiated onto the lightreceiving area 18a by a cycle number N_(min) which is equal to theminimum number of exposure light pulses. That is, when pulsed exposureis carried out at points P1, P2, . . . PN (N is an integer larger than2) in a range within, for example, the width of the exposure area 16 onthe locus Ti, the number N is equal to N_(min). Further, during thescanning of the light receiving area 18a on each locus Ti (i=1 to n),the calculating device 8 shown in FIG. 1 integrates signals U deliveredfrom the illumination sensor 18 in the number N_(min) which is thenumber of light pulses, at every pulsed exposure, so as to obtain anintegrated U_(di).

FIG. 4 shows an array in which the thus integrated output signals U_(di)are arranged, corresponding to Y_(i) in the Y-coordinate system, anunevenness among the integrated output signals U_(di) shown in FIG. 4,exhibits an unevenness which possibly occurs over the entire surface ofeach shot area on the wafer in the case of the exposure by the scanexposure system, that is, an unevenness in the possibly occurring worstintegrated exposure value. It is noted that those which can correspondto an actual distribution are obtained by normalizing the integratedoutput signals U_(di) with the output signals from the integrator sensor7, and accordingly, the distribution of the integrated exposure valuesshown in FIG. 4 does not precisely correspond to the distribution ofactual integrated exposure values in the nonscanning direction. Further,also in FIG. 5, although the component due to an unevenness in speed, anemission jitter or the like is not normalized so that it does notprecisely coincide with the distribution of unevennesses in exposure, asatisfactorily approximated solution can be given.

It is noted that although the minimum number N_(min) of exposure pulsesis previously set in the above-mentioned embodiment, the minimum numberN_(min) of exposure pulses may be determined from the result of themeasurement of an unevenness in the integrated exposure value bycarrying out the measurement shown in FIG. 3. That is, an unevennessamong the integrated output signals U_(di) is set to ΔE_(max), and thenumber of exposure pulses irradiated onto the illumination sensor 18during the measurement, is set to N. Further, an evenness ΔE_(th) inexposure caused by an evenness in pulse energy can be obtained from anunevenness among integrated output signals Si obtained from theintegrator sensor 17 at every scan along each locus Ti, and accordingly,the component ΔE_(ot) of the unevenness in exposure caused by scanexposure can be exhibited as follows:

    ΔE.sub.ot =(ΔE.sub.max.sup.2 -ΔE.sub.th.sup.2).sup.1/2EX5

Further, if an allowable unevenness among the integrated exposure valuesin the nonscanning direction is set to ΔE_(max) ', since ΔE_(th)=(δp/p)/N^(1/2) can be given, the minimum number N_(min) of exposurepulses can be determined by an integer which satisfies the followingexpression, corresponding to the expression EX4:

    N.sub.min ≧N·ΔE.sub.th.sup.2 /(ΔE.sub.max '.sup.2 -ΔE.sub.ot.sup.2)                           EX6

In this case, if the minimum number N_(min) of exposure pulses isgreater than the integer N, the scanning speed of the wafer stage 17 isdecreased or the emission period of the excimer laser source 1 isshortened so as to satisfy the above-mentioned expression EX6. Further,if the minimum number N_(min) of exposure pulses is smaller than theinteger N, the integer number N is used as the minimum number N_(min) ofexposure pulses.

Next, explanation will be made of a method of precisely measuring adistribution of integrated exposure values in the nonscanning direction.Also in this case, as shown in FIG. 3, the light receiving area 18a ofthe illumination sensor 18 scans the slit-like exposure area 16,successively along a plurality of loci T1 to Tn which are parallel withthe X direction or the scanning direction, and output signals U_(i)which are delivered from the illumination sensor 18, corresponding tothe number N_(min) of exposure pulses at every scanning cycle, areintegrated by the calculating device 8 shown in FIG. 1 so as to obtainthe integrated output signal U_(di). Further, simultaneously with thescanning operation of the illumination sensor 18 along each of the lociTi (i=1 to n), output signals S from the integrator sensor 7 shown inFIG. 1 are integrated by the calculating device 8 by a numbercorresponding to the number N_(min) of exposure pulses so as to obtainan integrated output signal S_(i). Then, the integrated output signalU_(di) from the illumination sensor 18 is normalized by dividing theintegrated output signal U_(di) from the illumination sensor 18, withthe integrated output signal S_(i) of the integrator sensor 7.

FIG. 5 shows an array in which the thus normalized integrated outputsignals U_(di) /S_(i) from the illumination sensor 18 are lined up inthe nonscanning direction, corresponding to Y_(i) of each locus Ti inthe Y coordinate system. The affection caused by an unevenness in thereproducibility of emission energy from the excimer laser source 1during the scanning of the illumination sensor 18 along each locus Ti isremoved from the result shown in FIG. 5. However, the data of thenormalized integrated output signals U_(di) /S_(i) include an affectionby an unevenness in the speed of the wafer stage 17, and an affection bythe reproducibility of a jitter of the pulse emission timing of theexcimer laser source 1. It is noted that the affection by an unevennessin the speed and the affection by the reproducibility of a jitter of thepulse emitting timing of the excimer laser source 1 are less in generalunless the control conditions of the wafer stage 17 and the excimerlaser source 1 become worse than those in the normal condition.Accordingly, an unevenness (which is the standard deviation σ or threetimes as large as this value) among the normalized integrated outputsignals U_(di) /S_(i) in the nonscanning direction, as shown in FIG. 5,can be regarded as an unevenness in the integrated exposure value in thenonscanning direction, which occurs in each shot area on the wafer W inthe case of actual exposure by the scan exposure system onto the wafer Wcoated thereover with photoresist.

Thus, according to this embodiment, with the repetitions of the scanningof the illumination sensor 18 over the slit-like exposure area 16, andonly by normalizing the integrated output signal from the sensor 18 withthe integrated output signal from an integrator sensor 7, it is possibleto precisely measure an unevenness among the integrated exposure valueson the wafer W in the nonscanning direction.

Next, explanation will be hereinbelow made of another embodiment of thepresent invention with reference to FIG. 6. A projection exposureapparatus used in the embodiment is substantially similar to that shownin FIG. 1, except that a line sensor including charge-storage typephoto-electric conversion elements (illumination sensor 21) is used, asshown in FIG. 6, instead of the illumination sensor 18.

Referring to FIG. 6 which shows an illumination sensor 21 used in thisembodiment, the illumination sensor 21 is composed of a one-dimensionalcharge-coupling type image pick-up device (CCD) having a sensitivity todeep-ultraviolet radiation, and having light receiving pixels 22₁ to22_(M) (M is an integer greater than n) which are lined up in the Ydirection or the nonscanning direction. In this embodiment, in order tomeasure an unevenness among the integrated exposure values on the waferW, the illumination sensor 21 scans the slit-like exposure area 16, oncein the X direction (or -X direction) at a maximum speed during exposure,and accumulated signals are read out from a series of the lightreceiving pixels in the illumination sensor 21 after the scanning.

In this case, those of the pixels in the illumination sensor 21 whichcross the exposure area 16 along loci T1 to Tn which are substantiallythe same as the loci T1 to Tn shown in FIG. 3 are present, andaccumulated signals read from light receiving pixels which have passedthrough a locus nearest to the locus Ti (i=1 to n), after the scanning,are denoted as U_(di). In this phase, pulse exposure can be made atpoints P1 to PN (N is equal to the minimum number N_(min) of exposurepulses) on, for example, the locus T1. However, since the illuminationsensor 21 is not subjected to scanning as a one unit body, pulseexposure is carried out simultaneously for other loci T2 to Tn.Accordingly, the distributions of the accumulated signals U_(di) in thenonscanning direction, which are obtained corresponding to the loci Tishown in FIG. 6, commonly include an unevenness in the speed of thewafer stage 17, and an affection by the reproducibility of a jitter ofthe emission timing of the excimer laser source 1.

Thus, the distributions of the accumulated signals U_(di) obtained fromFIG. 6, are coincident with an unevenness among the integrated exposurevalues in the nonscanning direction which are obtained through theactual exposure by the scan exposure system onto the wafer W coatedthereover with photoresist. Further, since the measurement can becompleted only the one-time scanning of the illumination sensor 21,thereby it is possible to shorten the time of measurement. It is notedthat an unevenness among the sensitivities of the light receiving pixelsin the illumination sensor 21 which is of a line sensor type should becompensated to a sufficiently small value with respect to a value to bemeasured.

Although the above-mentioned embodiments use a pulse light source, thepresent invention can also be applied directly to a scan type exposureapparatus using a continuous light source such as a mercury lamp, as theexposure apparatus.

Thus, the present invention should not be limited to the above-mentionedembodiments, but can take various arrangements without departure fromthe general concept of the present invention.

In view of the above-mentioned exposure unevenness measuring method,since the integrated values of output signals from measuringphoto-electric conversion means which has actually scanned, are directlyused as they are, it is advantageous to measure a maximum value ofunevenness which occur on the substrate in the case of the exposure bythe scan exposure system.

Further, in the case of the normalization by dividing the integratedvalue of output signals from the measuring photo-electric conversionmeans with the integrated value of output signals from referencephoto-electric conversion means, it is possible to measure an unevennessin exposure which occurs on the substrate during the exposure by thescan exposure apparatus in the nonscanning direction.

Further, an unevenness in exposure which occurs on the substrate in thecase of the exposure by the scan exposure system in the nonscanningdirection can be measured at a high speed only by one-time scanning ofthe line sensor type measuring photo-electric means.

Further, with the use of an unevenness measured by the method ofmeasuring an unevenness in exposure, the minimum number of exposurepulses for confining unevennesses in exposure within an allowable rangecan be determined.

What is claimed is:
 1. An exposure method comprising the stepsof:providing a slit-like illumination light beam for illuminating a maskon which a pattern is formed so as to form an image of said pattern on asubstrate by scanning said mask and said substrate in a scanningdirection; performing a scanning operation with a sensor in whichphoto-electric signals are obtained from said sensor while moving saidsensor in said scanning direction and relative to said slit-likeillumination light beam; repeating the scanning operation with saidsensor after moving said sensor in a direction orthogonal to saidscanning direction; integrating said photo-electric signals obtainedfrom said sensor for each respective scanning operation; and calculatingan unevenness among integrated values of said photo-electric signalsrelating to a direction orthogonal to said scanning direction.
 2. Amethod according to claim 1, wherein said sensor moves at a maximumspeed during the scanning operations.
 3. A method according to claim 1,wherein said illumination light beam has a trapezoidal distribution ofillumination on said substrate with respect to said scanning direction.4. A method according to claim 1, wherein a value related to at leastone photo-electric signal from said sensor is divided by a value relatedto at least one output signal from a monitoring sensors, which receiveslight split from said illumination light beam, so as to obtain anormalized integrated value for each scanning operation.
 5. A methodaccording to claim 1, wherein said illumination light beam is in theform of exposure pulses, and photo-electric signals which are deliveredfrom said sensor during emission of a minimum number of said exposurepulses are integrated.
 6. An exposure apparatus comprising:anillumination optical system for illuminating a mask on which a patternis formed, with a slit-like illumination light beam; a mask stage formoving said mask; a substrate stage for moving a substrate on which animage of said pattern is formed; a drive device for scanning said maskand said substrate relative to said slit-like illuminating light beam; asensor provided on said substrate stage; a controller for controllingsaid drive device so as to move said substrate stage in a scanningdirection, so that said sensor can perform a scanning operation, and ina direction orthogonal to said scanning directions, to position saidsensor for another scanning operation; and a calculating device forcalculating an integrated value of output signals from said sensor foreach respective scanning operation and for calculating an unevennessamong the integrated values relating to said direction orthogonal tosaid scanning direction.
 7. A method of measuring an intensity ofillumination, used in a manufacture of a semiconductor device,comprising the steps of:providing a slit-like illumination light beamfor illuminating a substrate from which said semiconductor device isformed; performing a scanning operation with a sensor in whichphoto-electric signals are obtained from said sensor while moving saidsensor in a scanning direction and relative to said slit-likeillumination light beam; repeating said scanning operation with saidsensor after moving said sensor in a direction orthogonal to saidscanning direction; integrating said photo-electric signals obtainedfrom said sensor during each respective scanning operation; andcalculating an unevenness among integrated values of said photo-electricsignals relating to the direction orthogonal to the scanning direction.8. An exposure method comprising the steps of:providing a slit-likeillumination light beam for illuminating a mask on which a pattern isformed so as to form an image of said pattern on a substrate by scanningsaid mask and said substrate; performing a scanning operation with anarray sensor having a plurality of photo-electric conversion elementsarrayed in a direction orthogonal to the scanning directions, in whichoutput signals are obtained from said plurality of photo-electricconversion elements while moving said array sensor in a scanningdirection with respect to the slit-like illumination light beam;integrating photo-electric signals which are obtained from saidphoto-electric conversion elements, respectively; and calculating anunevenness among integrated values of said photo-electric signalsrelating to a direction orthogonal to said scanning direction.
 9. Amethod according to claim 1, wherein said sensor scans at apredetermined speed relating to said scanning direction during thescanning operation.
 10. An exposure apparatus comprising:a mask stagefor carrying a mask on which a pattern is formed; an illuminationoptical system for illuminating the mask with a slit-like illuminationlight beam; a substrate stage carrying a substrate on which an image ofsaid pattern is formed; a drive device to scan said mask and saidsubstrate relative to said slit-like illumination light beam; a sensorprovided on said substrate stage and having a plurality of lightreceiving elements which are arranged thereon in a direction across ascanning direction; a control system to control said drive device so asto move said sensor in said scanning direction relative to saidslit-like illumination light beam; and a calculation circuit tointegrate photo-electric signals from said plurality of light receivingelements, respectively.
 11. An exposure apparatus according to claim 10,wherein said calculation circuit calculates an unevenness amongintegrated exposure values on said substrate relating to said directionacross said scanning direction based on a plurality of integratedphoto-electric signals.
 12. An exposure apparatus according to claim 11,wherein said illumination light beam is in a form of pulses, and saidcalculation circuit calculates a minimum number of pulses to illuminatesaid substrate based on said unevenness among said integrated exposurevalues.
 13. An exposure apparatus according to claim 6, wherein saidillumination light beam is in a form of pulses, and said calculatingdevice calculates a minimum number of pulses to illuminate saidsubstrate based on said unevenness among said integrated values.
 14. Anexposure method according to claim 1, wherein said illumination lightbeam is in a form of pulses, and said sensor is moved in said scanningdirection at a maximum speed for every said scanning operation during anemission of a minimum number of exposure pulses of said illuminationlight beam.
 15. A method of measuring an illumination unevenness,comprising:illuminating a slit-like illumination area with a pulse lightbeam, wherein said slit-like illumination area has a plurality ofpartial areas disposed along a direction substantially orthogonal to ascanning direction; scanning a sensor in said scanning direction on asubstrate stage relative to said slit-like illumination area to obtain apulse energy of a plurality of pulse light beams; and obtaining anintegrated value of said pulse energy for each of said partial areas.16. A method according to claim 15, further comprising:measuring saidillumination unevenness relating to said direction substantiallyorthogonal to said scanning direction based on the integrated values ofsaid pulse.
 17. A scanning exposure method comprising the stepsof:providing pulsed beams used for an exposure operation in which saidpulsed beams illuminate a mask having a pattern so as to form an imageof said pattern on a substrate by moving said mask and said substratesynchronously in a scanning direction; and performing a scanningoperation with a sensor in which said sensor is moved in said scanningdirection and relative to said pulsed beams, during said scanningoperation, and receives N pulsed beams, wherein N is an integer.
 18. Amethod according to claim 17, wherein during said scanning operation, Nis determined in accordance with an unevenness in energy at every pulsedbeam.
 19. A method according to claim 17, further comprising the step ofobtaining information regarding unevenness in an integrated exposurevalue occurring in said exposure operation, in accordance with a resultof said scanning operation with the sensor.
 20. A method according toclaim 17, wherein during said scanning operation, said sensor moves inan image plane of the pattern image of said mask or in a plane in thevicinity of said image plane.
 21. A semiconductor device which isproduced by using a scanning exposure method recited in claim
 17. 22. Ascanning exposure method in which a pattern of a mask is transferredonto a substrate while moving the mask and the substrate synchronouslyin a scanning direction relative to an exposure beam, the methodcomprising the steps of:directing said exposure beam to an illuminationarea; detecting an energy of said exposure beam in each of a pluralityof positions along said scanning direction in said illumination area;and integrating the detected energies.
 23. A scanning exposure methodaccording to claim 22, wherein said pattern of said mask is transferredonto said substrate through a projection optical system and saidillumination area is formed on an image plane side of said projectionoptical system.
 24. A scanning exposure method according to claim 22,wherein said step of detecting an energy of said exposure beam isperformed by moving a sensor relative to said illumination area alongsaid scanning direction.
 25. A scanning exposure method according toclaim 24, wherein said sensor comprises a single receiving element. 26.A scanning exposure method according to claim 24, wherein said sensor isa line-sensor comprising a plurality of receiving elements arrangedalong said scanning direction.
 27. A scanning exposure method accordingto claim 22, wherein a result of said integrating step is information onan integrated exposure value with respect to said substrate.
 28. Ascanning exposure method according to claim 22, furthercomprising:performing said detecting step and said integrating step in aplurality of positions along a direction orthogonal to said scanningdirection.
 29. A scanning exposure method according to claim 28 whereina result of said integrating step corresponding to said plurality of thepositions along the direction orthogonal to said scanning direction isinformation on a distribution, in the direction orthogonal to saidscanning direction, of integrated exposure values with respect to saidsubstrate.
 30. A scanning exposure method according to claim 22, whereinsaid illumination area is in a shape of a rectangular slit.
 31. Ascanning exposure method according to claim 22, wherein said exposurebeam is a pulsed beam.
 32. A scanning exposure method according to claim22, wherein said exposure beam has a sectional intensity distribution onthe illumination area in the scanning direction and the intensitydistribution has a slope portion at an edge of the exposure beam.
 33. Asemiconductor device which is produced by using a scanning exposuremethod recited in claim
 22. 34. A scanning exposure method in which apattern of a mask is transferred onto a substrate while moving the maskand the substrate synchronously in a scanning direction relative to anexposure beam, the method comprising the steps of:directing saidexposure beam to an illumination area; moving a sensor for detecting anenergy of said exposure beam along said scanning direction relative tosaid illumination area; and integrating the energies detected in themovement of said sensor.
 35. A scanning exposure method according toclaim 34, wherein said pattern of said mask is transferred onto saidsubstrate through a projection optical system, and said illuminationarea is formed on an image plane side of said projection optical system.36. A scanning exposure method according to claim 34, wherein a resultof said integrating step is information on an integrated exposure valuewith respect to said substrate.
 37. A scanning exposure method accordingto claim 34, further comprising:performing the detecting of the energyand said integrating step in a plurality of positions along a directionorthogonal to said scanning direction.
 38. A scanning exposure methodaccording to claim 37, wherein a result of said integrating stepperformed in said plurality of the positions along the directionorthogonal to said scanning direction is information on a distribution,in the direction orthogonal to said scanning direction, of integratedexposure values with respect to said substrate.
 39. A scanning exposuremethod according to claim 34, wherein said illumination area is in ashape of a rectangular slit.
 40. A scanning exposure method according toclaim 34, wherein said exposure beam is a pulsed beam.
 41. A scanningexposure method according to claim 40, wherein said sensor detects apredetermined number of pulsed beams while passing through saidillumination area, and wherein said predetermined number is determinedin accordance with a number of pulsed beams irradiating said substratewhen said pattern of said mask is transferred onto said substrate.
 42. Ascanning exposure method according to claim 34, wherein a moving speedof said sensor is determined in accordance with a moving speed of saidsubstrate when said pattern of said mask is transferred onto saidsubstrate.
 43. A scanning exposure method according to claim 34, whereinsaid sensor comprises a single receiving element.
 44. A scanningexposure method according to claim 34, wherein said sensor is aline-sensor comprising a plurality of receiving elements arranged alonga direction orthogonal to said scanning direction.
 45. A scanningexposure method according to claim 34, wherein said exposure beam has asectional intensity distribution on the illumination area in thescanning direction and the intensity distribution has a slope portion atan edge of the exposure beam.
 46. A semiconductor device which isproduced by using a scanning exposure method recited in claim
 34. 47. Ascanning exposure apparatus which transfers a pattern of a mask onto asubstrate while moving the mask and the substrate synchronously in ascanning direction relative to an exposure beam, the apparatuscomprising:a beam source which emits said exposure beam; a directingmember, disposed between said beam source and said substrate, whichdirects said exposure beam to an illumination area; a sensor, disposedon an exit side of said directing member, which detects an energy ofsaid exposure beam in each of a plurality of positions along saidscanning direction in said illumination area; and a calculator,connected to said sensor, which integrates the detected energy.
 48. Ascanning exposure apparatus which transfers a pattern of a mask onto asubstrate while moving the mask and the substrate synchronously in ascanning direction relative to an exposure beam, the apparatuscomprising:a beam source which emits said exposure beam; a directingmember, disposed between said beam source and said substrate, whichdirects said exposure beam to an illumination areas; a sensor, disposedon an exit side of said directing member, which moves relative to saidillumination area along said scanning direction to detect an energy ofsaid exposure beam; and a calculator, connected to said sensor, whichintegrates the detected energy during movement of said sensor.
 49. Amethod of making a scanning exposure apparatus which transfers a patternof a mask onto a substrate while moving the mask and the substratesynchronously in a scanning direction relative to an exposure beam, themethod comprising the steps of:providing a beam source which emits saidexposure beam; providing a directing member, disposed between said beamsource and said substrate, which directs said exposure beam to anillumination area; providing a sensor, disposed on an exit side of saiddirecting member, which detects an energy of said exposure beam in eachof a plurality of positions along said scanning direction in saidillumination area; and providing a calculator, connected to said sensor,which integrates the detected energy.
 50. A method according to claim49, wherein the detection of an energy of said exposure beam isperformed by moving said sensor relative to said illumination area alongsaid scanning direction.
 51. A method according to claim 49, whereinsaid sensor comprises a single receiving element.
 52. A method accordingto claim 49, wherein said sensor is a line-sensor comprising a pluralityof receiving elements arranged along a direction orthogonal to saidscanning direction.
 53. A method according to claim 49 wherein a resultof the integration is information on an integrated exposure value withrespect to said substrate.
 54. A method according to claim 49, whereinsaid exposure beam is an excimer pulsed beam.
 55. A method of making ascanning exposure apparatus which transfers a pattern of a mask onto asubstrate while moving the mask and the substrate synchronously in ascanning direction relative to an exposure beam, the method comprisingthe steps of:providing a beam source which emits said exposure beam;providing a directing member disposed between said beam source and saidsubstrate, which directs said exposure beam to an illumination area;providing a sensor, disposed on an exit side of said directing member,which moves relative to said illumination area along said scanningdirection to detect an energy of said exposure beam; and providing acalculator, connected to said sensor, which integrates the detectedenergy during movement of said sensor.
 56. A method according to claim55, wherein said sensor comprises a single receiving element.
 57. Amethod according to claim 55, wherein said sensor is a line-sensorcomprising a plurality of receiving elements arranged along a directionorthogonal to said scanning direction.
 58. A method according to claim55, wherein a result of the integration is information on an integratedexposure value with respect to said substrate.
 59. A method according toclaim 55, wherein said exposure beam is an excimer pulsed beam.
 60. Amethod according to claim 55, wherein said sensor detects apredetermined number of pulsed beams while passing through saidillumination area, and wherein said predetermined number is determinedin accordance with a number of pulsed beams irradiating said substratewhen said pattern of said mask is transferred onto said substrate.
 61. Amethod according to claim 55, wherein a moving speed of said sensor isdetermined in accordance with a moving speed of said substrate when saidpattern of said mask is transferred onto said substrate.